Furnace hearth



a. E. coNNoLLY 2,221,076

FURNACE HEARTH Nov; 12,1940.

Filed July 20, 1940 s Sheets-Sheet i v INVENTOR.

GEORG'EE CONNOLLK ATTORNEYS Nov. 12, 1940.

E. CONNOLL Y FURNACE HEARTH Filed July 20, 1940 5 Sheets-Sheet 2 K s me w m n *1 1m w m 2% N ww m G wm v i I 1 G. E. CONNOLLY 2.2 1.076

- FURNACE HEARTH Filed July 20, 1940 3 Sheets-Sheet 3 INVENTOR."

GEoRcEECo/v/voLLx ATTORNEYS Patented Nov. 12,

PATENT OFFICE.

azzime 1 FURNACE HEARTH George E. Connolly, Oakland, Calif., assignor to Nichols Engineering & Research Corporation, New York, N. Y., a corporation of Delaware Application July 20, 1940., Serial No. 346,543

2 Claims.

This invention relates to. hearth constructions of a type'particularly adapted for use in high temperature furnaces, or furnaces wherein the temperatures vary within wide limits from time 5 to time, or'vary widely' at one area as compared with other areas.

The objects of the invention include the provision of an improved hearth construction which will be relatively inexpensive and simple to manufacture and install and which will be durable and capable of withstanding temperature con- 'ditions such as above mentioned over substantially longer periods of time than possible with prior furnace hearth constructions. Various further and more specific objects, features and advantages will clearly appear from the detailed description given below taken in connection with the accompanying drawings forma ing a part of this specification and illustrating by way of examples, certain preferred forms of the invention. The invention consists in such novel features, arrangements and combinations,

as may be shown and described in connection with the constructions herein disclosed. I In the drawings, Fig. 1 is a vertical sectional view through a portion of a furnace embodying several superposed hearths constructed in accordance with the invention;

Fig. 2 is an enlarged plan view showing a secalong the line'6--6 of Fig. 5.

In the example of the invention as shown in Fig. 1, a plurality of circular hearths as at It],

of a so-called Herreshoff type of multiple hearth furnace, including a cylindrical'wall as at, l3 for enclosing the furnace and supporting the hearths, I

also including a central rotatable shaft as at llcarrying rabble arms as at I5 having teeth cooperating with each 'hearth. That is, as the rabbling structure rotates, the material on hearth l0, for example, will berabbled outwardly, wher'eby it will finally fall from hearthlllthrou'gh peripheralopenings'as at It on to hearth H.

tor of one of the hearths embodying the inven- Fig. 6 is a sectional view taken substantially H and I2 may be superimposed to form a parthearth II the rabbling teeth are so arranged that the material will be gradually advanced toward the central area of the hearth from which it may fall through opening I8 on to hearth I2. Hearth l2 may be similar in construction and 5 purpose, to hearth I0.

Referring now to Figs. 2 and 3, the improved construction of a typical out hearth such as hearth III will now be described. As here shown, the construction is adapted for a furnace having 10 a diameter of about 16 ft.'9 in. The hearth may be made up of a plurality of circles of refractory blocks. For example, withthe particular.construction shown, the blocks are arranged in six concentric circles to form the main part of the hearth, the number of blocks for each circle beingpreferably approximately as indicated on the drawings in Fig. 3, and varying from 36 to '76. The blocks are so shaped and arranged that the upper surface IQ of the hearth, except at 0 its inner rim, will conform rather accurately to a slightly conical surface, the inclination being for example A in. per twelve inches of radius, as indicated in Fig. 3. Also the blocks are'so shaped that the lower surface 20 of the hearth will conform to a slightly more conical surface, for example 1 in. per foot, as also indicated in Fig. 3. This will result in a hearth having a gradually increased thickness toward its peripheral portion, thus not only affording greater strength where the loads are most severe at the peripheral areas, but also this added thickness at the periphery will' serve to protect the blocks against deterioration from slagging effects caused by oil burners which are often placed beneath the peripheral portions of the hearths. Also this increased thickness will of course afford/deeper areas of contact between adjacent blocks wherethereof. Thus in order that all of the blocks'of the main portionof the hearth may be in gen era] of approximatelythe same wightand thic'k ness, each succeeding circle outwardly ,of "the hearth will embed?- a substantiallyinereas ed num-f "5'5 spalling under high temperatures is increased, for

the reason that laminations due to ramming the tile molds will be along vertical confined planes instead of planes parallel to the upper and lower surfaces of the hearth. That is, the mold'for each tile will normally be filled by ramming the material into the mold in a direction perpendicular to the largest surface area of the tile, with the consequence that any resulting laminations will v be parallel to the plane of such surface. Hence with the tiles positioned on edge in forming the hearth, the laminations will be in vertical planes, and thus confined under pressure in each circle of blocks, preventing separation of the laminations.

The innermost circle of blocks as at 2! may have its innermost circumferential surfaces inclinedupwardly and inwardly as at 22, and this circle may be adapted to receive a metal luting ring if desired as at 23, and/or a series of refractoryblocks as at 24 having inclined outerf'aces may be provided to form the luting ring, for cooperating with suitable luting members as at 25 (Fig. 1) carried by the shaft M, for preventing the material under treatment from falling down between the inner edge of this hearth and the rotating shaft l4. The circles of blocks 26-30 inclusive as shown may all have substantially fiat upper and lower surfaces and vertical side surfaces at suitable slight angles with respect to each other, whereby radially extending joints are provided between abutting side surfaces of the blocks of each circle. The circumferential or end surfaces of each of these blocks, as best shown in Fig. 3, are such that succeeding joints, outwardly of the furnace, be-

tween the abutting surfaces will be at progres-- sively increasing angles in respect to the vertical.

For'instance, as indicated in ,Fig. 3, the abutting circumferential blocks of circles 2| and 26 may be at an inclination (directed upwardly and outwardly of the hearth) amounting to 1 in. per foot. Similarly, each succeeding joint outwardly of the hearth is at an increased angle such that the outer surfaces of the blocks of circle 30, for

, instance, are at an inclination of 2% in. per foot.

With this construction the radial dimension at the top surface of each circle will be substantially greater than the radial dimension at the bottom surface of each circle, and thus each block and each of the circles of blocks will be substan- 0 tially keyed in position against the possibility that any one of the blocks or circles will slip down under varying temperature conditions. I

The furnace may be surrounded by an outer sheet metal cylindrical shell as at 3| preferably 65 providedwith a reinforcing band as at 32 opposite each hearth. As shown in the embodiment of Figs. 2 and 3, skew blocks as at 33 may be located at regions between each pair of hearth openings "l6, these skew blocks having their outer surfaces 70 abutting the metallic furnace shell 3|. These skew blocks may be supplemented by smaller blocks as at 34, and additional blocks of trapzoidal shape as at 35. The abutting circumferential surfaces of blocks 35, 34 and 33 respectively may 75 be at progressively increasing inclinations, as insurfaces between the,

as to not injure the blocks. substantial importance in cases such as where fuel dicated in Fig. 3, to provide an efiective keyed relationship, as in the case of the blocks of the hearth circles. Each of the blocks 35 may be so positioned as to abut, at its inner circumferential surface, a pair of wedge-shaped blocks as at 36 forming a part of the circle 30. -Each pair of theblocks 36 may alternate with a pair of oppositely directed wedge-shaped blocks asat 31.

" This arrangement provides a very stable and secure construction, notwithstanding the presence 10 of the large hearth openings I6.

In constructing the furnace, after the cylindrical metallic shell of the furnace is erected, the

' inner wall therefor may be gradually built up with suitable insulating material or blocks as at 15 38 and refractory lining material or blocks as at 39. When the level of a hearth such as hearth I0 is reached, the skew blocks as at 33 are first cemented in place. A suitable removable frame for supporting the hearth during its construction 26 may be put in place and the blocks such as at 34 and 35 are then put in place with joints to; adjacent blocks cemented. The blocks as at 33, 3! of the outermost circle 30 are then put in place and the last of these blocks to be inserted, for example one of the blocks 31, may be formed with side surfaces slightly wedge-shaped, whereby when the block is driven downwardly toward the temporary hearth supporting frame, it will be wedged into position and tend to expand the 30 circle 3!! somewhat, into firm engagement with the blocks 35 and with the blocks 36, 31 firmly engaging each other. Thereafter each of the succeeding circles of blocks 29, 28, etc., may be similarly put in place one after another, the 35 final block of each circle being driven or wedged into position so that each circle will be firmly .keyed to the succeeding outer circle.

The side surfaces of all of the blocks may be cemented together, with a suitable high tempera 40 ture resistant-bonding cement, except that along certain lines such as line 40 dividing the hearths into sections or quadrants,.the cement may be omitted, this in effect permanently dividing the hearth into sections or sectors. To prevent 45 cement from getting into the joints of these lines of separation, thin strips of paper may be inserted as along the line, 40 during assembly of the' hearth: With the hearth thus effectively divided into sections, in the event one section is 50 expanded or contracts more than others, then a slight movement of one section with respect to the others is possible, without danger of irregular cracking of various blocks or joints between blocks. Instead, each section of the hearth is 55 free for slight movement in respect to adjacent sections along definite predetermined lines preferably continuous and radial, and in such a manner This feature is of burners may be arranged at widely spaced. positions around the periphery of the hearth, thus causing uneven heating thereof, or in cases where burners may be applied to one edge of the hearth while burners at the opposite edge are extinguished. a

At various places around the wall of the furnace between each pair of hearths, inspection openings may be provided through the furnace wall, the dotted lines at 4| indicating the limits of one such opening.

In erecting the steel furnace shell, especially for large furnaces it may be difficult to so install the same that its diameter will be uniform as distinguished from being only roughly surface of such shell, difficulties would be encenter of the furnace and the spaces countered in locating all of the hearth circles in truly concentric relationship, as desired with respect to the central shaft of the furnace. To avoid these difficulties, where the furnace shell is of only approximately uniform diameter, the skew-back blocks as at 33' of Fig. 4 may be made somewhat smaller in their radial dimension, whereby space as at 42 is provided between the outer circumferential surfaces of these blocks and the interior of the furnace shell. With this construction all of the skew-back blocks 33' may be-put in place at a uniform distance from the 42 may be thereafter filled in with Portland cement grout.

The construction of a typical in hearth such as hearth H, is shown in Figs. 5 and 6 and may comprise for example five concentric circles of blocks, the outermost of which engages 'a' circle of skew-back blocks mounted within the furnace wall. The construction and arrangement of the inner circles 26-30' as shown" in these figures will be planation of the construction of these circles 26-49 of Fig. 2, as above described. In the circle of skew blocks of Fig. 5, blocks such as at 43 may stop short of the furnace shell 3| as shown, and the intervening space 42 may be filled with cement grout as in Fig. 4. However, skew-back blocks as at 44 and 45 which are located above or below a wall opening as at 4| are preferably cut on the job so as to substantially accurately fit the inside surface ofthe furnace shall without the intervening layer of 5, one of the dry cement. As shown in Fig. joints witho-t cement, for dividing the hearth into sections, :may be provided along the line 40'.

Where multiple hearth furnaces of the above indicated type are operated constantly and continuously over long periods of time at temperatures which .are not exceedingly high, and so that the hearthsare .not subjected to wide temperature variations, not much dimculty is encountered wi-th hearth constructions of types heretofore known.

However, when such furnaces are used for example, for the calcining of lime at temperatures in the neighborhood of 1800 F. and where the furnace is operated at intervals with frequent shut-down periods, the resulting expansion and contraction of the tion of prior known hearth constructions.

more conical lower surface, and

understood from the above ex- 'hearths tendsto cause serious cracking or slippingof blocks and resulting general deteriora- However, with the above described constructions, these difficulties'may be effectively eliminated.

While the inventionhas been described in detail with respect to particular preferred examples, it will be understood by those skilled in the art after understanding the invention that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended therefore in the appended claims to cover all such changes and modifications.

What is claimed'as new and desired tobe secured by Letters Patent is: i

1. A hearth construction for high temperature furnaces, comprising refractory blocks shaped and arranged to form a circular hearth with a slightly conical upper surface and a somewhat an annular se' ries of skew-back blocks surrounding the hearth and embraced by a cylindrical metallic furnace wall, the hearth areas including a plurality of concentric rings formed of the blocks, the blocks of each ring being wedged in a circumferential direction to expand the ring and maintain same under pressure against the next outer ring, the blocks being shaped to provide between adjacent rings, abutting surfaces which at succeeding rings outwardly of the hearth are at progressively increasing angles to the vertical, whereby the circumferential surfaces of the blocks of each ring are keyed in respect to the next inner and outer rings. 3

2. A hearth construction for high temperature furnaces, comprising in combination, refractory blocks shaped and arranged to form a circular hearth with self-supporting central arch areas including a plurality of concentric rings of blocks, the hearthbeing formed with a plurality of drop-holes around its periphery,

hearth and maintained by the skew-back blocks l under pressure in a direction tending to wedge apart the blocks of said outermost ring, so as to tend to expand the ring.

GEORGE E. CONNOILY. 

